I had an egg-eating problem for a while, and couldn't figure out which chicken was guilty.
Then one day, I saw a blue-jay flying out of the fenced-in run area. At first I thought the blue-jay was just filling up on pellets, but then later that week, I went it to the coop and caught her flying out of the coop-nesting boxes!

So a blue-jay had acquired a taste for eggs! Then I put up garden bird netting around the chain-link run enclosure, and haven't had a broken egg since.